1. Field of the Invention
The present invention relates to a rotation angle sensing device for taking in an output of a crank angle sensor, which senses multiple sensed portions rotating in synchronization with rotation of a crankshaft of an internal combustion engine, to sense a rotation angle of the crankshaft.
2. Description of Related Art
A known rotation angle sensing device of this type senses a rotation angle of an output shaft (crankshaft) by sensing multiple teeth (sensed portions) formed on a rotor, which is provided on the crankshaft, at an equal interval based on an output of a crank angle sensor. Usually, the intervals among the actual teeth have a structural error. The structural error can cause an error in sensing of the rotation angle of the crankshaft.
Therefore, for example, a device described in JP-A-H11-247707 senses time necessary for rotation of a section defined by two teeth and compares the sensed time with theoretical time to sense an angle error between the two teeth. One rotation range of the crankshaft is divided into multiple sections in accordance with the teeth, and the theoretical time is defined for each one of the divided sections. With this device, even if the rotation speed of the crankshaft cyclically changes in a cycle of 360° CA, influence of the cyclic change can be eliminated when the angle error is sensed.
However, the actual rotation speed of the crankshaft does not necessarily change cyclically in the cycle of 360° CA. Therefore, a difference between the sensed time and the theoretical time contains an influence of rotation fluctuation of the crankshaft that does not have the cycle of 360° CA. The angle error sensed by this device contains the influence of the rotation fluctuation of the crankshaft that does not have the cycle of 360° CA. As a result, it is difficult to sense the angle error at high accuracy. Moreover, this device has to prepare the theoretical time for sensing the angle error, complicating the manufacturing process of the device.
Another rotation angle sensing device is described also in JP-A-H10-122031 or JP-A-H10-73613.